1. Field of the Invention
The present invention relates to a magnification calibration apparatus and a shape measurement system, and more particularly, to a magnification calibration apparatus and a shape measurement system that can calibrate the magnification of an interference optical system for interference measurements.
2. Discussion of the Related Art
In interference measurements, diffraction or the like causes fictitious rises (edges) at the peripheral of a 3D graphic representation of an object surface (a graphic representation in which the shape of the object surface is expressed in three dimensions), which is obtained by analytic means, such as a fringe scan. Therefore, the resultant data do not faithfully indicate the surface profile of object surface. Accordingly, a so-called edge removing function has been used to correct this error.
Furthermore, depending on the reflectivity of the object surface, the strength of the brightness signal from the interference fringes may become insufficient as a result of mis-match between the light reflected from reference surface of the interferometer and the light reflected from the object surface. In order to cope with such variations in the brightness signal, a function is provided for automatically adjusting the gain of the interference fringe image pickup device.
However, if the significant edge effects occur or surfaces with different reflectivities are measured, the effective area of the object surface that is detected by the interference fringe image pickup device varies from object surface to object surface, even if the actual diameters of the object surfaces are the same. Accordingly, when discrete intervals, at which the profile of the object surface is sampled by the interference fringe image pickup device, are set with reference to the outer diameter as a standard, undesirable errors may be generated.